The present invention relates to data storage devices, such as hard disk drives, and more particularly to techniques for identifying servo sectors in data storage devices.
Magnetic recording disk drives incorporate stacked, commonly-rotated rigid magnetic recording disks that are used for storing user data. The data is recorded in radially-spaced data tracks on the surfaces of the disks. Recording heads are moved by an actuator in a generally radial path toward and away from the center of rotation of the disks to read and write data on the disks. Typically, a single recording head, which may be an inductive read/write head or an inductive write head in combination with a magneto resistive read head, is associated with a corresponding magnetic recording surface of each disk.
It is important to know the precise radial and circumferential location of the recording heads relative to their associated disk surfaces. For conventional fixed-block architecture disk drives, position information is typically recorded onto the disk as servo information in angularly spaced servo sectors interspersed among the data sectors.
Each of the servo sectors contains a servo timing mark (STM), which is a defined bit pattern. A servo timing mark is also known as a servo identification (SID) or a servo address mark (SAM). When an STM is identified in reading the disk, subsequent detection of servo information (e.g., track identification and position error signal bursts) is initiated. This servo information is used by servo electronics to determine the radial position of the head and to provide feedback to the actuator to ensure the head remains positioned over the centerline of the desired track. In many disk drives, it is beneficial for the drive to determine the STM as quickly as possible following movement of the head, to speed read and write operations.
The servo information follows the STM. A disk drive can identify the servo information once the STM is found. Accurate detection of STMs is important for being able to correctly recognize subsequent servo information. If a servo sector is not recognized due to failure to detect the STM, the servo electronics relies on less recent servo information (e.g., from the most recently recognized servo sector), and servo tracking and timing accuracy is diminished.
The servo information includes, for example, the PHSN (physical head sector number). The PHSN indicates the number of the current servo sector that is being read by the read head. Each servo sector in a track on a disk includes a unique PHSN relative to the other servo sectors in that track. The PHSN allows a disk drive to distinguish a servo sector from each of the other servo sectors in the same track. The PSHN is followed by the track identification (TID).
Several bits are typically stored in each servo sector to provide a PHSN. As a result, recording a PHSN in each servo sector uses a significant amount of additional disk storage space. Furthermore, even more bits need to be stored in each servo sector to provide protection against errors in the PHSNs.
Therefore, it would be desirable to provide a technique for improving the reliability of servo identification patterns that does not significantly reduce the data storage capacity of the disk.